I'm now riding my old, beater 1967 Schwinn "Typhoon" with the huge, messanger-stlye basket on the front of it to work every day. I'm even running errands on it as well. Man, do those 4.1 miles (each way) seem a lot longer and a HELL OF A LOT HARDER on that thing, especially with a head wind. Still, the down hills are worth it. There is nothing like bombing a hill on an old tanker bike. Nothing.
Which reminds me, if you ever get the chance to rent (buy or borrow) a copy of the documnetary, Klunkerz do it! It pretty much covers the history of the Mountain Bike (which was done right here in Marin County)and is really interesting and fun. My buddy, John Pedersen's group; the Road Oilers has more than a few tunes in it and I even know a handful of the kooks in the film that were there (inadvertantly) making history.
As for me opting to ride the balloon tire bike over my titanium/carbon fiber bike is so typical of me trying to keep it simple. It seems most things in my life: transportation, surfing or whatever; One Fin, One Gear, One Kid, One World. I like it.